Unified model for authoring and executing flow-based and constraint-based workflows

ABSTRACT

Designing and executing a workflow having flow-based and constraint-based regions. A user selects one or more activities to be part of a constraint-based region. Each constraint-based region has a constraint associated therewith. The workflow is executed by executing the flow-based region and the constraint-based region. The flow-based region executes sequentially. The constraint is evaluated, and the constraint-based region executes responsive to the evaluated constraint.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/046,988 filed Jan. 31, 2005, which claims the benefit of U.S.Provisional Patent Application No. 60/615,542 filed Oct. 1, 2004, bothof which are herein incorporated by reference in their entirety.

TECHNICAL FIELD

Embodiments of the present invention relate to the field of workflowmodeling. In particular, embodiments of this invention relate to acomponentized and extensible workflow model.

BACKGROUND

Existing systems attempt to map business problems to high-levelworkflows by modeling the business problem. However, real worldworkflows vary in a variety of dimensions such as (a) execution andmodeling complexity, (b) knowledge of the structure of the flow atdesign time, (c) statically defined or ad-hoc/dynamic, (d) ease ofauthoring and editing the flow at various points in its lifecycle, and(e) weak or strong association of business logic with the core workflowprocess. Existing models fail to accommodate all these factors.

Further, most existing workflow models are based on eitherlanguage-based approaches (e.g., BPEL4WS, XLANG/S, and WSFL) orapplication based approaches. Language based approaches are high-levelworkflow languages with a closed set of pre-defined constructs helpmodel the workflow process to the user/programmer. The workflowlanguages carry all of the semantic information for the closed set ofconstructs to enable the user to build a workflow model. However, thelanguages are not extensible by the developers and represent a closedset of primitives that constitute the workflow model. The languages aretied to the language compiler shipped by the workflow system vendor.Only the workflow system product vendor may extend the model byextending the language with a new set of constructs in a future versionof the product. This often requires upgrading the compiler associatedwith the language.

Application based approaches are applications which have the workflowcapabilities within the application to solve a domain specific problem.These applications are not truly extensible nor do they have aprogrammable model.

With the existing approaches, the issues of complexity, foreknowledge,dynamic workflows, authoring ease, and strength of associations withbusiness logic and core workflows are not adequately addressed. Thereare no extensible, customizable, and re-hostable workflow designerframeworks available to build visual workflow designers to modeldifferent classes of workflows. Existing systems lack a rapidapplication development (RAD) style workflow design experience whichallows users to graphically design the workflow process and associatethe business logic in a programming language of developer's choice. Inaddition, there are no ink-enabled workflow designers.

In addition, existing systems fail to provide seamless ad-hoc or dynamicediting for executing workflows. Workflow processes are dynamic andmobile in nature and their form cannot be entirely foreseen at designtime. The workflow processes start in a structured fashion andeventually evolve and change during the course of their executionlifetime. There is a need for a workflow authoring framework that allowsworkflow builders to author various types of workflow models at designtime as well as make ad-hoc or dynamic changes to running workflows in aseamless manner. Even after a workflow process has been deployed and isrunning, changes in business requirements often force changing orediting the currently running workflow process. There is a need for asystem that provides runtime authoring of a workflow process.

In addition, workflow processes deal with cross cutting orthogonal andtangled concerns that span multiple steps of a workflow process model.For example, while parts of the workflow process are designed toparticipate in long running transactions, other parts of the sameprocess are designed for concurrent execution. Still other portions ofthe same workflow process require tracking, while other portions handlebusiness or application level exceptions. There is a need to applycertain behaviors to one or more portions of a workflow process.

Some workflow modeling approaches are impractical as they require acomplete flow-based description of an entire business process includingall exceptions and human interventions. Some of these approaches provideadditional functionality as exceptions arise, while other approachesexclusively employ a constraint-based approach instead of a flow-basedapproach to modeling a business process. Existing systems implementeither the flow-based or constraint-based approach. Such systems are tooinflexible to model many common business situations.

Accordingly, a componentized and extensible workflow model is desired toaddress one or more of these and other disadvantages.

SUMMARY

Embodiments of the invention provide an extensible framework forbuilding a componentized workflow model. In particular, each step of aworkflow process has an associated component model that describes designtime aspects, compile time aspects, and runtime aspects of the workflowstep. Further, any developer may extend the core workflow model byauthoring these components. The invention includes a workflow enginethat is flexible and powerful enough to coordinate the execution ofvarious kinds of workflows including highly formal machine-to-machineprocesses, constraint-based ad-hoc human workflows, and workflows havinga mixture of flow-based and constraint-based approaches. The workflowengine permits activation, execution, query, and control capabilitiesagainst executing workflows. For example, the invention permits ad-hocand dynamic changes to executing workflows. The workflow engine isrehostable or embeddable in a variety of host environments includingboth server and client environments. Each specific host environmentmarries the workflow engine to a set of service providers. The aggregatecapabilities of the service providers determine the kinds of workflowsthat may be executed in the specific host environment.

Other embodiments of the invention provide a declarative format such asan extensible orchestration markup language (XOML) for serializing aworkflow model. The declarative format enables a user to extend theworkflow model by writing a set of components. The semanticscorresponding to the various steps of a workflow process areencapsulated in an activity validator component which validates andenforces the semantics for a given component at compile time.Embodiments of the declarative format of the invention further enablethe declaration and association of data with various elements of theworkflow model. The declarative format supports the transformation ofthe data through the workflow. For example, the format representsexternal data sources such as databases or files, code snippets, andbusiness rules within the workflow model declaratively.

An embodiment of the invention provides an extensible, customizable, andre-hostable workflow designer framework to build graphical/visualworkflow designers to model different classes of workflows. Anotherembodiment of the invention supports a rapid application developmentstyle workflow design experience to allow users to graphically design aworkflow process and associate business logic in any programminglanguage. Embodiments of the invention also provide ink support usingpen and tablet technologies. The invention provides a free form drawingsurface in which a workflow drawn by a user is converted into aninternal representation. The invention supports creation andmodification of the workflows via ink editing on the existing drawingsurface (e.g., add/delete activities), and ink annotation of existingworkflows (e.g., comments, suggestions, or reminders hand-drawn on thedesign surface).

Still other embodiments of the invention provide components forcapturing cross cutting behaviors in a declarative way and applying thebehaviors to selected portions of a workflow model. Other embodiments ofthe invention execute the selected portions of the workflow model in thecontext of the behaviors associated therewith. Embodiments of theinvention provide a framework, reusable components, and a language todeal with cross cutting orthogonal and tangled concerns that spanmultiple steps of a workflow process model.

In accordance with one aspect of the invention, a computer-implementedsystem represents a workflow model. The computer-implemented systemincludes a workflow having a structured plurality of activities. Theworkflow further includes an unstructured plurality of activities eachhaving a constraint associated therewith. The system also includes aruntime engine for performing the workflow by executing each of thestructured plurality of activities, evaluating the constraint for eachof the unstructured plurality of activities, and executing each of theunstructured plurality of activities as a function of evaluating theconstraint associated therewith.

In accordance with another aspect of the invention, a method models aworkflow. The workflow represents a business process. The methodincludes presenting a plurality of activities to a user. The method alsoincludes receiving from the user a selection of the presented activitiesand a flow specification associated therewith. The method also includesgrouping the received selection of activities in accordance with thereceived flow specification. The method also includes receiving from theuser another selection of the presented activities and a constraintassociated therewith. The method also includes merging the receivedother selection of the presented activities with the grouped selectionof activities to create a workflow.

In accordance with yet another aspect of the invention, one or morecomputer-readable media have computer-executable components for modelinga workflow having a flow-based region and a constraint-based region. Thecomponents include a display component for presenting a plurality ofactivities to a user. The components also include an interface componentfor receiving from the user a selection of the presented activities anda flow specification associated therewith. The interface componentfurther receives from the user another selection of the presentedactivities and a constraint associated each therewith. The componentalso includes a designer component for grouping the received selectionof activities in accordance with the received flow specification. Thedesigner component further merges the received other selection of thepresented activities with the grouped selection of activities to createa workflow.

Alternatively, the invention may comprise various other methods andapparatuses.

Other features will be in part apparent and in part pointed outhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary workflow containing tasks and control flowcomposite activities.

FIG. 2 illustrates an exemplary activity inheritance tree.

FIG. 3 illustrates an exemplary component model.

FIG. 4 illustrates an exemplary component model lifecycle.

FIG. 5 is a block diagram illustrating a constrained activity groupwithin a flow-based workflow.

FIG. 6 is a high-level application user interface for authoringworkflows that relies upon wizards for specification of the workflow.

FIG. 7 illustrates an exemplary workflow designer.

FIG. 8 illustrates an orchestration program including a receive activityfollowed by a send activity.

FIG. 9 illustrates a schedule definition and the relationship between avisual workflow, a serialized representation in XOML of the workflow,and the code beside of the workflow.

FIG. 10 is a block diagram illustrating one example of a suitablecomputing system environment in which the invention may be implemented.

Appendix A describes exemplary activities.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

Embodiments of the invention model a workflow representing a processsuch as a business process. Business processes are dependant and orderedtasks, activities, or the like that result in predictable and repeatableoutcomes. Including an organization's operating procedures,institutional working knowledge, and information resources, businessprocesses are designed to satisfy defined business objectives in anefficient and timely manner. In an efficient environment, the functionalcomponents of a process can be readily identified, adapted, and deployedto address ever-changing corporate requirements. The workflow is an enduser's experience interacting with the tasks in a business process.Tasks are modeled as activities, components, or the like, eachrepresenting a unit of work that is performed by a person or machine. Inone embodiment, a plurality of activities is presented to a user. Theuser selects and organizes the activities to create the workflow. Thecreated workflow is executed to model the business process. Referring toFIG. 1, an exemplary workflow 100 contains tasks and control flowcomposite activities.

In one example, an orchestration engine workflow model supportsmodeling, authoring and executing different classes of workflows.Examples include modeling a given problem in terms of a structured setof steps that occur in an ordered sequence or as a set of asynchronousevents. The orchestration engine coordinates the execution of schedules.A schedule is an organized set of activities that is arrangedhierarchically in a tree structure. The execution context of, and theshared data visible to, an executing activity is provided by a scope.Each activity represents a component that encapsulates metadata for thestep in a workflow process. The activity is the basic unit of executionin the workflow model and has associated properties, handlers,constraints and events. Each activity may be configured by user code inany programming language. For example, the user code may representbusiness or application logic or rules written in common languageruntime (CLR) languages. Each activity supports pre-interception hooksand post-interception hooks into execution in the user code. Eachactivity has associated runtime execution semantics and behavior (e.g.,state management, transactions, event handling and exception handling).Activities may share state with other activities. Activities may beprimitive activities or grouped into a composite activity. A primitiveor basic activity has no substructure (e.g., child activities), and thusis a leaf node in a tree structure. A composite activity containssubstructure (e.g., it is the parent of one or more child activities).

In one embodiment, activities are of three types: simple activity,container activity and root activity. In this embodiment, there is oneroot activity in the model, and none or any quantity of simpleactivities or container activities inside the root activity. A containeractivity may include simple or container activities. The entire workflowprocess may be used as an activity to build higher-order workflowprocesses. Further, an activity may be interruptible ornon-interruptible. A non-interruptible composite activity does notinclude interruptible activities. A non-interruptible activity lacksservices that would cause the activity to block.

The orchestration engine provides an exemplary set of activities.Referring to FIG. 2, an activity inheritance tree illustrates exemplaryactivities. The exemplary activities listed in FIG. 2 are described indetail in Appendix A. In addition, any user may write one or moreactivities to extend the workflow model. For example, the user may writeactivities for a specific business problem, domain, workflow standard(e.g. business process execution language), or a target platform. Theorchestration engine may provide a rich set of services to the user forwriting activities which include, for example, services of analyzingcode, type resolution and type system, services for serialization, andrendering.

In one embodiment, each activity has at least three parts: metadata,instance data, and execution logic. The metadata of the activity definesdata properties that may be configured. For example, some activities mayshare a common set of metadata defined in an activity abstract baseclass. Each activity declares its own additional metadata propertiesaccording to its needs by extending this class.

The values of metadata properties will be shared by all instances ofthat activity across the instances of the schedule where the activitywas configured. For example, if a user creates a schedule A and adds asend activity to it, the send activity is given identificationinformation (e.g., “001”) as part of its metadata. A second sendactivity added to the schedule would receive its own uniqueidentification information (e.g., “002”). Once multiple instances ofschedule A are created and executed, all instances of send “001” willshare metadata values. In contrast, the instance data of an activitydefines a set of data which is specific to the instance of the activityin a running schedule instance. For example, a delay activity may offera read-only property on its instance data that is the date and timevalue representing the delay activity's timeout value. This value isavailable once the delay activity has begun executing, and it is mostlikely different for every single instance of the delay activity. It iscommon to refer to instances of schedules, and especially instances ofactivities and tasks, without qualifying the reference with “instance.”

Composite activities have their set of child activities as anotherelement. Child activities are considered metadata in one embodiment. Theorchestration engine model explicitly permits manipulation of thismetadata at runtime within an instance of the schedule. It is possibleto add new child activities to a composite activity that is part of anexecuting schedule instance such that only the metadata (activity tree)for that schedule instance is affected.

Referring next to FIG. 3, each activity has an associated set ofcomponents that forms the component model for the activity. Theassociated set of components includes an activity executor, an activitydesigner, an activity serializer, an activity validator (e.g., semanticchecker), and an activity code generator. The activity executor is astateless component that implements the execution semantics for theactivity. The activity executor works with the metadata of an activityto implement the activity. A core scheduler acts as a service providerfor the activity executor to provide services to the activity executor.

The activity designer visually displays the design time visualrepresentation of the activity. The activity designer is a node in adesigner hierarchy and may be themed or skinned. The activity designeris hosted in a design environment (e.g., an application program) andinteracts with the host design environment via services. The activityvalidator enforces the activity semantics at compile time as well asruntime. The activity validator operates on the context of the workflowmodel and uses the services provided by the environment (e.g., compiler,designer, or runtime). Validation occurs at various points in thelifecycle of a workflow. Structural compliance checks are made whencreating serialized representations of the workflow, when compiling, andin response to the user's request. The semantic checks may be strongerat runtime than those performed at compile-time to ensure the safety ofa runtime operation such as the addition or replacement of an activityin the activity tree of a running instance. The invention evaluatessemantics associated with each of the activities for conformance orcompliance with, for example, predefined interface requirements.

The activity serializer is a component that serializes the metadata ofan activity. The activity serializer is called from the variousmodel/format serializers. The entire workflow model is serialized basedon an extensible schema into a declarative markup language which may befurther translated into other workflow languages as desired.

In one embodiment, the component model for an activity is stored as adata structure on a computer-readable medium. In the data structure, theactivity designer is represented by an image field storing data (e.g.,an icon) for visually representing the activity. In addition, one ormore author time fields store metadata defining properties, methods, andevents associated with the activity. The activity serializer isrepresented by a serializer field storing data for transferring themetadata stored in the author time fields to a declarativerepresentation of the activity. The activity generator is represented bya business logic field storing software code associated with themetadata stored in the author time fields. The activity executor isrepresented by an executor field storing data for executing the softwarecode stored in the business logic field.

Scopes and Schedules

The execution context of, and the shared data visible to, an executingactivity is provided by a scope. A scope is one of the core activities.A scope is a unifying construct for bringing together variables and thestate of a long-running service with transactional semantics,error-handling semantics, compensation, event handlers, and data statemanagement. A scope may have associated exception and event handlers. Inone embodiment, a scope may be transactional, atomic, long running, orsynchronized. Concurrency control is provided for the user in cases ofconflicting read-write or write-write access to user variables. A scopeis also a transaction boundary, an exception handling boundary, and acompensation boundary. Since scopes may be nested within a schedule, itis further possible to declare variables, messages, channels, andcorrelation sets with the same name in different scopes (even if thescopes are nested) without name collision.

Scopes nested within a schedule are only executable within the contextof that schedule. A schedule may be compiled either as an application(e.g., a standalone executable entity) or as a library (e.g., forinvocation from other schedules). Every schedule that is compiled as alibrary effectively constitutes a new activity type that may be invokedfrom within other schedules. A schedule's metadata includes thedeclaration of parameters.

Once a schedule is developed, instances of the developed schedule may beexecuted. The process of activating and controlling a schedule instanceis a function of the host environment in which the orchestration engineis embedded. The orchestration engine provides a no-frills “simple host”that may be used to test schedules. In addition, the orchestrationengine provides an activation service to promote standardization of a“service provider” model (e.g., application programming interfaces) thatis used alike by the engine and external applications for interactingwith the service environment (i.e. host). The activation service createsa schedule instance of a particular schedule type, optionally passingparameters. The schedule instance is essentially a proxy to the runningschedule instance and includes an identifier that uniquely identifiesthe instance, a reference to the metadata (activity tree) for theschedule, and methods to suspend, resume, and terminate the instance.The activation service also support finding a schedule instance based ona given schedule instance identifier.

Code-Beside

A scope activity may have an associated code-beside class that includesbusiness logic for the scope activity. Since a schedule is itself ascope, a schedule may also have a code-beside class. Any scopes nestedwithin a schedule may also have their own code-beside classes. Theactivities that are nested within a scope share the scope's code-besideclass which acts as a container for their shared data state and businesslogic. For example, metadata for a code activity includes a reference toa method with a particular signature in the code-beside. In anotherexample, metadata for a send activity includes an optional reference toa code-beside method of a particular signature plus mandatory referencesto a message declaration and a channel declaration.

Exemplary uses of code-beside include the following: declaration ofvariables, messages, channels, and correlation sets; declaration ofin/out/ref parameters; declaration of additional custom properties;preparation of a message to be sent; processing of a message that hasbeen received; implementation of a rule expressed in code that returns aBoolean value; manipulation of locally defined variables; readingactivity metadata and instance data; writing activity instance data(e.g., setting a property on an activity about to be executed); raisingan event; throwing an exception; enumerating and navigating thehierarchy of activities in the running schedule instance's activitytree, including across nested scopes and schedule invocation boundaries;adding new activities to a composite activity within the runningschedule instance; changing the declarative rules associated withactivities within the running schedule instance; and obtainingreferences to, and manipulating, other running schedule instances.

Referring to FIG. 4, a block diagram illustrates an exemplary componentmodel lifecycle. A user interacts with computer-executable componentsstored on one or more computer-readable media for modeling a workflowhaving a flow-based region and a constraint-based region. Thecomputer-executable components include a display component 402, aninterface component 404, a designer component 406, and a runtimecomponent 408. The display component 402 presents a plurality ofactivities to a user. The interface component 404 receiving from theuser a selection of the presented activities and a flow specificationassociated therewith. The designer component 406 groups the receivedselection of activities in accordance with the received flowspecification to create a structured plurality of activities. Theinterface component 404 further receives from the user another selectionof the presented activities and a constraint associated each therewith.This other selection represents an unstructured plurality of activitieseach having a constraint associated therewith. In one embodiment, theuser defines one or more of the constraints. The designer component 406further merges the structured plurality of activities with theunstructured plurality of activities to create a workflow. The runtimecomponent 408 executes the structured plurality of activities inaccordance with the flow specification. The runtime component 408further executes the created workflow by evaluating the constraintassociated with each of the unstructured plurality of activities andexecuting those activities whose constraint has been satisfied per theevaluation. In one embodiment, the constraint has an input parameter andthe runtime engine 408 further performs the workflow by identifying achange in the input parameter and re-evaluating the constraint.

In one embodiment, one or more of the display component 402, interfacecomponent 404, designer component 406, and runtime component 408 executewithin an execution environment, context, or the like, of an applicationprogram.

Hardware, software, and a system such as illustrated in FIG. 4 anddescribed herein constitute exemplary means for presenting to the userthe structured plurality of activities and the unstructured plurality ofactivities; exemplary means for receiving from the user a selection ofthe structured plurality of activities, a selection of the unstructuredplurality of activities, and a flow specification associated with theselected activities; exemplary means for grouping the selection of thestructured plurality of activities and the selection of the unstructuredplurality of activities in accordance with the flow specification tocreate the workflow; and exemplary means for executing the createdworkflow.

One or more computer-readable media have computer-executableinstructions for performing the method.

Constrained Activity Groups

Workflows come in many shapes and sizes and each may be characterized bywhere it sits on a spectrum ranging from ad-hoc at one end to formal atthe other. In general, an ad-hoc workflow has a set of tasks to beperformed or executed in any order. That is, the set of tasks areindependent with respect to execution order. A formal workflow haswell-defined control flow constructs (e.g., sequencing, concurrency,conditional branching, and while loops) used to precisely define andcontrol the execution of the set of tasks. Some workflows have partswhich are formal and other parts which are ad-hoc and most easilyexpressed as having goals and constraints. In some cases, workflows mayeven migrate along this spectrum during their lifetime or have theirflow and/or constraints change while instances are in-flight.

The invention provides the unification of flow-based scheduling andconstraint-based scheduling. This synthesis centers around a controlflow construct called constrained activity group (CAG). The CAG activityprovides a grouping of activities whose course of execution is guided byconstraints associated with the contained activities. In this way, CAGfacilitates goal oriented constrained execution of a set of activities(e.g., related activities) in which paths of execution are notexplicitly modeled. The degenerate case of CAG (e.g., in which noconstraints are specified on any of the contained activities and thedefault completion condition is utilized) is unsynchronized concurrentor parallel execution of the contained activities.

The CAG is associated with a completion condition that declares whenexecution of the CAG is considered complete. An exemplary defaultcompletion condition declares execution of the CAG to be complete whenall contained activities are in the complete or cancelled state. Anexemplary completion condition is a Boolean value that referencesvariables and messages in the scope enclosing the CAG and its parentscopes as well as the state of other activities. If the completioncondition evaluates to true when the CAG moves from the latent state tothe enabled state, then the CAG immediately completes without enablementor execution of any contained activities. When the completion conditionof an executing CAG activity evaluates to true at any time, any and allexecuting activities contained within the CAG are immediately cancelledand the CAG activity moves to the completed state.

Each activity in the CAG has an associated constraint associatedtherewith. An exemplary constraint for a constrained activity (e.g., onewithin the CAG) is a Boolean function that references variables andmessages in the scope enclosing the CAG and its parent scopes, but notsibling scopes, as well as the state of other activities within the CAG.A constraint may be either transparent, partially transparent, or opaquedepending upon what is known about its data dependencies andimplementation. Data dependencies, but not implementation, are known fora partially transparent constraint. For a fully transparent constraint,data dependencies and implementation are known. Opaque constraints donot offer information about either data dependencies or implementation.Transparent and partially transparent constraints have the advantage ofmore efficient evaluation since the engine may make useful judgmentsabout when the evaluation of such a constraint is required.

An enable constraint on an activity, when it becomes true, declares thatthe associated activity is ready for execution and must be enabled. Thisconstraint is only meaningful while the activity is in the latent state.Thus, it may only evaluate to true once. A constraint may be disabled atany time after it has been enabled. This supports the XOR conditioncommon in the case where two tasks are assigned to two individuals, thecompletion of one cancels the other task (disabled). The disableconstraint as in the enable constraint is a one-shot. The enableconstraint of a CAG may be re-enabled after the CAG's completioncondition is satisfied to provide a repeat semantic or a while semanticto the tasks in the CAG.

The completion condition of a CAG activity and all the constraintsassociated with contained activities may be thought of as a singlecollection of expressions. When the CAG itself is enabled, all Booleanexpressions whose data dependencies are satisfied are evaluated. If thecompletion condition of the CAG is true, then the CAG is immediatelyconsidered complete. Otherwise, a list of zero or more activities to beenabled is generated. The workflow engine of the invention enables theidentified activities. As changes occur to the state of the schedule(e.g., to the state of the data universe on which the constraints andcompletion condition depend) due to activity execution, re-evaluation ofconstraints occurs and new activities to be enabled are identified.Expression evaluation and activity execution are performed concurrentlyas opposed to a phased or two step iterative process.

Referring next to FIG. 5, a block diagram illustrates a workflow model500 having a constraint-based region defined within a flow-based regionusing a CAG. The flow-based region includes a structured set ofactivities (e.g., workflow model elements). The constraint-based regionof the workflow shows a set of activities which are performed when anassociated constraint (e.g., a Boolean expression over the data state ofthe schedule) is true. A flow-based model is complete when its endpointis reached while the activities within the constraint-based region areexecuted whenever a constraint associated with one of the activities issatisfied (e.g., indefinitely or until a CAG completion semantic issatisfied). Having a completion semantic for the constraint-based regionenables constraint-based regions and flow-based regions to be combined.

In the example of FIG. 5, the constraint-based region includesConstrainedGroup1 502. The activities within ConstrainedGroup1 includeSend1 5 04 and Delay1 506. Each of the activities 504, 506 have aconstraint associated therewith. In addition, a completion condition 508is associated with ConstrainedGroup1 502.

Workflow Stencils

A workflow stencil (e.g., a workflow template or an activity package)includes a root activity and a set of activities. Stencils may be domainand or host specific. Examples of the former include a structuredworkflow stencil, human workflow stencil, and an unstructured workflowstencil. Some stencils may be “closed” as a set of activities includingone or more roots designed to work together, possibly in a particularhost environment. Other stencils may be “open”, to varying degrees. Astencil defines its extensibility points. For instance, a developerwrites a CustomRoot and a new abstract CustomActivity and declares thatthe package is CustomRoot plus any activity that derives fromCustomActivity.

An exemplary BPEL or XLANG/S stencil includes a root activity with thefollowing characteristics: participates in state management andtransactions, has associated event and exception handlers, supportscontract first model, may be analyzed, and has well-defined activationand termination behavior. The exemplary stencil further includes a setof messaging specific activities (e.g., Send and Receive and theirvariants) and other structured activities such as Scope, Loop,Condition, Listen, and Throw.

An exemplary Halifax Stencil includes a root activity with the followingcharacteristics: implicit state management, associated exceptionhandlers (0-n), supports event-based model, has well defined activationbehavior, and has undefined termination. The root activity contains 0-nEventDriven activities. Each EventDriven Activity represents a HalifaxAction. Each EventDriven Activity has an associated state managementprotocol and executes in an atomic scope.

Designer Framework (User Interface)

The orchestration engine provides a framework for designing variousclasses of workflow models in a WYSWYG fashion. For example, referringto FIG. 6, a high-level application user interface for authoringworkflows relies upon wizards for specification of the workflow. Theframework includes a set of services and behaviors that enabledevelopers to write visual workflow designers. These services provide anefficient way of rendering a workflow process, support for Ink/Tabletfor drawing the flows, and support for designer operations such asundo/redo, drag/drop, cut/copy/paste, zoom, pan, search/replace,bookmarks, adornments, smart tags for validation errors, validdrop-target indicators for activities, auto layout, view pagination,navigation markers, drag indicators, print and preview withheaders/footers, etc. Through such a user interface, simple workflowscontaining tasks and control flow composite activities (e.g., sequence,parallel, and conditional) may be constructed. No input of code (orreliance upon existing compiled code) is required either for rulespecification (e.g., conditional branching logic, while looping logic)or dataflow specification (e.g., the output of task A is input to taskB). The serialized representation of a schedule (including rules anddataflow) is self-contained and complete in some scenarios where nocode-beside is required.

Using the designer framework of the invention, the orchestration engineof the invention includes a rapid application development (RAD) stylevisual workflow designer with support for associating software code withthe workflow model in a visual way. Each activity in the workflow has anassociated activity designer. Each activity designer is written in termsof framework services. The framework of the invention also contains avisual designer model. The visual designer model includes a set ofactivity designers linked with one another via relationships describedin the workflow model. FIG. 7 illustrates an exemplary workflowdesigner. The invention includes various modes of associating code withthe workflow model including “Code-Beside”, “Code-Within” and“Code-Only” which enables round-tripping of the user code to theworkflow model in real time. The invention also provides real-timesemantic errors while the user is building the workflow.

In one embodiment, the invention presents the user with a packageidentifying a plurality of activities in the designer framework userinterface. The invention further receives from the user a selection andhierarchical organization of the presented activities. The inventionserializes the received activities to create a persistent representationof the workflow. The invention further receives from the user softwarecode representing business logic for association with one of theplurality of activities in the workflow. The invention may also receivea user-defined activity having one or more semantics associatedtherewith. The invention includes a semantic checker or validator forevaluating the semantics for conformance to a predefined interfacerequirement. If the semantics conform to the predefined interfacerequirement, the invention presents the user-defined activity as one ofthe plurality of activities. The invention further compiles the softwarecode to create one or more binary files. For example, the inventioncompiles the serialized workflow representation and software code into asingle assembly containing an executable representation of the workflow.The invention executes the created workflow. In one embodiment, one ormore computer-readable media have computer-executable instructions forperforming the method.

The orchestration engine designer allows the user to recursively composehigher order schedules by using other created schedule and using them.The inline expansion of schedules allows the user to view the schedulecontents inline and cut or copy the contents. To enable the inlineexpansion of the schedule and to make the schedule read only, a separatedesign surface and designer host for the inline schedule is created.Further, the composite schedule designer has its own hierarchy. Theinvoked schedule is loaded and displayed when the designer is expandedby the user. In one embodiment, the designer is collapsed when theactivity is dropped or copied on the design surface. A property chainsthe calling activity designer with the root designer of the hostedschedule. The following functions prevent the adding and removing ofactivities from the designer.

internal static bool AreAllComponentsInWritableContext(ICollectioncomponents) internal static bool IsContextReadOnly(IServiceProviderserviceProvider)

These functions are called by the infrastructure to check if the contextin which the activities are being inserted is writable. For the hosteddesigner these functions return false. In addition, properties areprevented from being modified. Other functions fetch the activitydesigners from the appropriate components:

internal static ServiceDesigner GetSafeRootDesigner(IServiceProviderserviceProvider) internal static ICompositeActivityDesignerGetSafeParentDesigner(object obj) internal static IActivityDesignerGetSafeDesigner(object obj)

In one example, a user creates a schedule and compiles it as activity.On successful compilation, the schedule appears on the toolbox. The useropens or creates the schedule in which use of the compiled schedule isdesired. The user drags and drops the compiled schedule from thetoolbox. A collapsed schedule designer is shown on the design surface.When the user wants to view the contents of the compiled schedule whichwas dropped, the user expands the schedule designer to show the contentsof the invoked schedule inline in a read only state. The inlining of thecalled schedule enables the user to view the invoked schedule withoutswitching between different schedule designers. The feature is useful todevelopers composing higher order schedules by reusing existingschedules.

Support for Customization of the Designer Framework Using Themes/Skins

A workflow designer written using the designer framework may becustomized using workflow themes. These may be extensible markuplanguage (XML) files which declaratively describe various aspects of thedesigner. The workflow designer provides wizard support for partners toextend activities. Exemplary user interface features supported by theworkflow designer include, but are not limited to, undo/redo, drag/drop,cut/copy/paste, zoom, pan, search/replace, bookmarks, adornments, smarttags for validation errors, valid drop-target indicators for activities,auto layout, view pagination, navigation markers, drag indicators, printand preview with headers/footers, and document outline integration. Theworkflow designer supports custom designer themes/skins to enablecustomizing the look and feel of the designer using XML metadata. Theworkflow designer supports background compilation. In one example, smarttags and smart actions are provided for validation errors whiledesigning the schedule. The workflow designer may be hosted in anycontainer (e.g., application programs, shells, etc.).

An exemplary orchestration engine program includes a receive activityfollowed by a send activity. The process receives a message and sends itout. The user creates a project called “Hello World” and adds anorchestration item to the project. The user then drags and drops a scopeactivity onto the design surface. Next, the user drops a receiveactivity followed by a send activity onto the scope. FIG. 8 illustratesthe resultant workflow 800 in the designer. Each activity designerprovides a user interface representation on an object model. Developersare able to directly program the object model and set properties onactivities or use the designer. The orchestration engine designer allowsa developer to select an activity from the toolbox and drag it onto thedesigner surface. If the activity has already been placed into aschedule and needs to be moved, the developer is able to select it (byclicking on it) and drag it to the area of the schedule where it needsto go. If a developer hold the control key while dragging and dropping,a copy of the selected activities selected are made.

Active placement provides possible drop points (targets) as visualindicators on the design surface. Auto scrolling also participateswithin the context of drag and drop. When dealing with large schedules,navigation to areas of the designer currently not in the view port areaccessible by dragging the activity towards the area of the schedule tobe placed.

Drag and drop is supported across schedules in the same project andacross schedules in other projects in the same solution. After anactivity has been placed onto the design surface, the developerconfigures the activity. Each activity has a set of properties that adeveloper configures in order for the schedule to be valid. Theseproperties are editable in the property browser. Every activity controlswhat properties are viewable in the property browser. To aide thedeveloper in configuring various activities, the designer provides avariety of dialogs or “sub-designers”. Each of the dialogs is invokedfor various properties of activities.

The orchestration engine is able to customize the activities presentedin the toolbox. When a developer creates a custom activity or schedule,the end result is an assembly. Using a dialog, a developer is able tobrowse to the assembly location and select the assembly to make itappear as an orchestration engine activity. Alternatively, a developermay place the assembly in the orchestration engine installation path andit will be present as an orchestration engine activity.

Application Programming Interfaces (APIs)

In another embodiment, the invention provides application programminginterfaces (APIs) for performing various workflow operations. Theinvention includes a design application programming interface forauthoring the workflow. The design application programming interfacecomprises means for authoring a workflow and means for selecting one ormore of the activities to create the workflow. The invention alsoincludes a compilation application programming interface for compilingthe workflow authored via the design application programming interface.The compilation application programming interface comprises means forserializing the workflow, means for customizing a visual appearance ofthe workflow, means for compiling the workflow authored via the designapplication programming interface, means for validating the workflow.

The invention also includes a type provider application programminginterface for associating a type with each of the activities in theworkflow. The type provider application programming interface comprisesmeans for associating the type with each of the activities in theworkflow and means for associating a type with each of the activities inthe workflow.

One or more APIs constitute exemplary means for authoring the workflow,exemplary means for selecting one or more of the activities to createthe workflow, exemplary means for serializing the workflow, exemplarymeans for customizing a visual appearance of the workflow, exemplarymeans for validating the workflow, exemplary means for compiling theworkflow, and exemplary means for associating a type with each of theactivities in the workflow.

Activity Execution Framework

With the exception of schedule and scope, the engine views activities asabstract entities and simply coordinates the execution of activitieswithout knowing the specific data or semantics of any particularactivity. In one embodiment, four entities interact during the executionof an activity: the activity itself, a parent activity of the activitythat is executing, the scope enclosing the activity that is executing,and the orchestration engine. Each entity has a different function.

If the execute method of an activity returns without having signaledcompletion to its activity coordinator, the activity is said to be in alogical waiting state. Such an activity may be cancelled by theorchestration engine, or continued (e.g., once the item or event onwhich it is waiting becomes available or occurs, and the activity isnotified of this by the engine).

Some activities which never enter the logical waiting state may never becancelled. Examples include the send activity and the code activitysince they execute without any demands on external events orsubscriptions. Once handed a thread (i.e. once their execute method iscalled by the orchestration engine), these activities will do work untildone. The orchestration engine is never given an opportunity to cancelthem since they do not return the thread until they signal completion.

The orchestration engine runtime uses rules to trigger events on whichorchestration engine activities are executed. The orchestration enginedesigner provides the user ability to associated rules to be evaluatedat runtime to trigger events. The orchestration engine designer enablesthe user to use different types of rules technology by providingextensibility architecture. The designer is agnostic to the type ofrules technology used.

In one embodiment, the designer supports Boolean expression handlers asa way to associate a rule with an activity. This means that in the usercode file; the user writes a method which returns a true or false value;based on which the rule is triggered. Currently there are multipletechnologies which may also be used to evaluate rules including InfoAgent and Business Rules Engine (BRE). To achieve this, the designerincludes an extensibility architecture which enables the rule technologydevelopers to host custom user interfaces in the designer. The designerprovides a way to the custom user interface writers to serialize therules in the form of code statement collection. The designer emits aBoolean handler in user code file with the code statement collectionsinserted into it. The orchestration engine includes a default userinterface which may also be used by the rule writers. A rule technologyprovider add rules to the orchestration engine designer by creating acustom rule declaration, writing a user interface type editor associatedwith the custom rule declaration, creating a custom user interface tohost the rules user interface, and generating code statements on save.

In one example, a user selects the activity designer with which ruleneeds to be attached, locates the rule property in the property browserand selects the “RuleExpressionHandler” in the drop down (which makesthe “Statements” property to appear underneath the Rule Property in theuser interface), specifies the user code method name in the “Statements”property, invokes a user interface type editor to invoke a dialog whichwill host rules specific user interface, and defines rules in the dialogby creating new predicate rows and grouping them together. The userinterface emits a method in the user code file. The method name will besame as the one specified by the user in the property browser. The codestatements equivalent to creating the rule will be inserted in the usercode method for rule.

Messaging During Execution

In a running workflow, messages sent to a schedule are intended for aspecific schedule instance. For example, an invoice for purchase order#123 must be sent back to the same schedule instance that originated(e.g., sent out) that purchase order. To match an inbound message withthe appropriate schedule instance, the message and the schedule instanceshare a correlation set. The correlation set may be a single-valuedcorrelation set in which means an identifier field in the message ismatched against an identifier of the same type that is held by scheduleinstances. Multi-property correlation sets are also possible andanalogous to multi-column primary keys in a database table.

The correlation set value held by a schedule instance is initializedwhen the schedule instance sends out a message (e.g., the value may betaken from an identifier field of an outbound purchase order) orreceives a message. This correlation set value is then a part of thatschedule instance's state. When a subsequent inbound message arrives,the correlation set value held in the schedule instance state is matchedagainst the identifier held by an inbound message of the expected type.When a match is found, the correlation set is satisfied and the messageis delivered to the schedule instance.

Although the implementation of correlation sets is a function of theorchestration engine and host environment, the user in one embodimentdeclares the correlation sets to make the schedule instance workcorrectly. In another embodiment, some activities (e.g.,SendRequest/ReceiveResponse activities and ReceiveRequest/SendResponseactivities) set up the correlation sets independent of the user. A widerange of validation checks are performed by the send and receiveactivities to ensure that correlation sets are initialized and followedproperly.

Dynamic Editing of Executing Workflows

The orchestration engine provides a framework for authoring (andsubsequently visualizing and executing) various types of workflows.Examples include event-condition-action (ECA) style workflows orstructured flows or rules driven flows. Further, regardless of the waythe workflow was modeled, the framework allows the users to author oredit workflows in the same manner at design time or even when theworkflow process is running without the need for recompiling theworkflow process. The framework allows the user to roundtrip between theruntime and the design time representation with hi-fidelity. Ad hocchanges are the changes made at run time to the process model. A usermay ask a running instance for its schedule model and make changes tothe model. For example, the user may add, remove, or replace activitiesin a batch, then commit or rollback the batched changes. In oneembodiment, the model is validated after the updates. In many workflowscenarios of the invention, there is a blurring of, or even anelimination of, the separation between “design-time authoring” and“runtime execution.”

A schedule instance effectively shares with other instances the activitytype (metadata) tree defined for those instances' schedule type. But anyschedule instance, once it begins executing, may be changed on the flyvia the addition of new activities or the manipulation of declarativerules. It is possible to take such a modified schedule instance and“save as” as a new schedule type or more generally, to simply recoverthe serialized representation from the instance. That is, a runningschedule instance may be serialized and then brought into any designer(e.g., authoring environment) or runtime visualization tool.

Further, it is possible for an advanced developer to author a scheduleentirely as software code. To author a schedule type directly, thedeveloper simply includes a static method called InitializeScheduleModelin the software code in the code-beside class for the schedule and marksthis method with a [ScheduleCreator] attribute. In one embodiment, thestatic method takes no parameters and returns a Schedule object. Thereis no companion serialized file, though the serialized representation ofthe schedule may be recovered from the Schedule object that is created.Although this means that a schedule may be developed using a singlesoftware code file, validation checks may not be performed on the file.The orchestration engine compilation ensures the structural and semanticvalidity of the activity tree that underlies the schedule type. Inanother embodiment, compilation and validation run internally to producethe actual type that is executed, but no code input is required.Schedule type compilation becomes a very light process since there is notranslation from a compile-time object model to a runtime object model.In essence, compilation simply combines the object model representationof a schedule with code-beside to produce a new type. In one embodiment,there may be no fundamental need to provide any code-beside at all for aparticular schedule if the compiled code-beside matches what is demandedby the activities in the object model or code-beside may already existin compiled form (an assembly).

When compiling a serialized schedule, it is possible to point to anexisting compiled type that effectively serves as the code-beside forthe schedule. A derivative of this compiled type is created and this newtype serves as the code-beside to ensure that a unique type is createdto represent the new schedule.

Serialization Architecture

The serialization infrastructure provides a modular, format neutral andeasily extensible mechanism to serialize the orchestration engineactivity tree. In particular, a caller (e.g., an application program ora user) requests a serializer for an object (or activity) A from theserialization manager. The metadata attribute of object A's type bindsobject A to a serializer of the requested type. The caller then asks theserializer to serialize object A. Object A's serializer then serializesobject A. For each object encountered while serializing, the serializerrequests additional serializers from the serialization manager. Theresult of the serialization is returned to the caller.

Every activity in the orchestration engine component model mayparticipate in serialization. The serializer component is not a part ofactivity class itself in one embodiment. Instead the component isspecified by annotating a serializer attribute in a class associatedwith the activity. The serializer attribute points to a class which isused to serialize objects of that activity type. In another embodiment,provider components for an activity type override the default serializerprovided by the activity.

Designer serialization is based upon metadata, serializers, and aserialization manager. Metadata attributes are used to relate a typewith a serializer. A “bootstrapping” attribute may be used to install anobject that provides serializers for types that do not have them. Aserializer is an object that knows how to serialize a particular type ora range of types. There is a base class for each data format. Forexample, there may be an XmlSerializer base class that knows how toconvert an object into XML. The invention is a general architecture thatis independent of any specific serialization format. The serializationmanager is an object that provides an information store for all thevarious serializers that are used to serialize an object graph. Forexample, a graph of fifty objects may have fifty different serializersthat all generate their own output. The serialization manager may beused by these serializers to communicate with each other when necessary.

In one embodiment, the use of serialization providers coupled withserializers that use generic object metadata provide a callbackmechanism where an object is given the opportunity to provide aserializer for a given type. A serialization manager may be given aserialization provider through a method such asAddSerializationProvider. A serialization provider may be automaticallyadded to a serialization manager by adding an attribute such asDefaultSerializationProviderAttribute to the serializer.

In one embodiment, the format is dictated by the following rules: anobject is serialized as an xml element, a property of an object iscategorized as simple property (e.g., serialized as an xml attribute) orcomplex property (serialized as child element), and a child object of anobject is serialized as child element. The definition of a child objectmay differ from an object to another object. The example below is theserialization of a while activity, which has a Send activity as one ofits child objects.

<While ID=“while1”> <ConditionRule> <CodeExpressionRuleDeclaration><Expression Name=“whileCondition” /> </CodeExpressionRuleDeclaration></ConditionRule> <Send HasTypedChannel=“True” ID=“send1”><MessageName=“msg1” Type=“System.UInt32” /> <OnBeforeSendName=“onBeforeSend1” /> <TypedChannel Type=“System.Collections.IList”Operation=“AddIndex” Name=“Foo” /> </Send> </While>

In an embodiment in which the language used for serialization is XOML,each XOML element is serialized to its respective object when theschedule is compiled. Objects include both simple and complex types. Themapping between the XOML representation of each activity and its mappingto the authoring object model is next described. Serialization of XOMLvaries between Primitive and Composite activities.

Simple types for primitive activities are serialized as attributes onthe activity type. Complex types for primitive activities are serializedas child elements. As an example, here is the XOML representation of aSend activity.

<Send ID=“send1” HasTypedChannel=“False”> <MessageName=“message1”Type=“System.String” /> <UntypedChannel Name=“c1” /> </Send>

In a similar manner to primitive type serialization, simple types forcomposite activities are serialized as attributes on the activity type.However, by definition, composite activities encapsulate nestedactivities. Each nested activity is serialized as another child element.As an example, here is the XOML representation of a While activity.

<While ID=“while1”> <ConditionRule> <CodeExpressionRule> <ExpressionName=“test” /> </CodeExpressionRule> </ConditionRule> </While>

A strong relationship between the process/workflow view and theserialized representation exists. FIG. 9 illustrates a scheduledefinition and the relationship between a visual workflow, a serialized(e.g., XOML) representation of the workflow, and the code beside of theworkflow. When authoring in either representation, the other will incurchanges. Thus, modifying the XOML for an activity (or its constituentparts in cases of composite activities) is directly reflected in theprocess/workflow view when a developer switches between the two. Theconverse is also applicable. Modifying the activity in theprocess/workflow view results in the appropriate modification withinXOML. As an example, the deletion of an activity in the process/workflowview results in the removal of the XML element in XOML for the sameactivity. Round tripping also occurs between the process/workflow viewand the code beside.

During creation of the XOML code, if the XOML definition does notconform to a pre-defined interface requirement, the offending XMLelement is underscored or otherwise visually identified to thedeveloper. If the developer switches to the process view, they will bealerted that there is an error within the XOML and the designer providea link where the developer may click and will be navigated to theoffending element. This same error appears in the task pane and upondoubling clicking on the error, the developer will be navigated to theoffending element in the XOML.

Creating the Activity Tree from a XOML File (Deserialization)

In one embodiment, a CreateEditorinstance( ) function creates aDesignSurface object and then calls a BeginLoad( ) function onto theDesignSurface object passing the actual loader object into it, whicheventually ends up in a BeginLoad( ) call to a DesignerLoader( )function. A PerformLoad( ) function reads the text buffer object anddeserializes it to the orchestration engine component model hierarchy.The invention walks through the hierarchy and inserts the activitiesinto the design surface to load the components in the visual studio.

The invention also listens to changes to the XOML file to track thehierarchy and item identification changes to update the values in thevisual studio cache. A secondary document data list includes a list ofsecondary documents, invisible to the user, on which orchestrationengine designer works. For example, it is possible that user has notopened the code beside file, but when the user makes changes in theorchestration engine designer, the changes are made to the code besidefile. As this file is not visible to the user, the file is maintained asa secondary document. Whenever the XOML file is saved, the secondarydocuments are automatically saved. If the name of one of these fileschanges or if the file is deleted, the invention updates thecorresponding secondary document objects accordingly.

Exemplary deserialization guidelines for an object tree are as follows.An xml element is first treated as a property of parent object. If theparent object does not have a property with the element's tag name thenthe element is treated as a child object of the parent object. An xmlattribute is treated as simple property on the parent object.

In an exemplary deserialization using the serialized code above, a<While> element is treated as an object created using the xml namespaceinformation. A <ConditionRule> element is treated as a property of theWhile activity. The <CodeExpressionRuleDeclaration> element is treatedan as object whose value will be applied to the ConditionRule property.The <Send> element is first tried as a property of the While activity,but the ‘While’ activity does not have a property with the name ‘Send’,so the <Send> element is treated as an object and added as the childrenactivity of the while activity. The <Message> element is treated as aproperty of the Send activity. Because the Message property on Send isread only, the contents of Message element are considered as thecontents of Message object. A similar rule applies to thedeserialization of <OnBeforeSend> and <TypedChannel> elements.

Under the following conditions, XOML de-serialization will criticallyfail: the XOML code is not well formed, the XomlDocument is not thefirst element in the XOML code, and the first activity in the XOML codecannot be de-serialized. The developer will be presented with errormessage with which they may navigate to the offending XML element whenswitching from XOML view to process/workflow view.

Hosting the Orchestration Engine Designer

The designer framework may be hosted in any application program. This isa very useful feature for third party applications to render workflow intheir respective environments. It also will allow third parties todevelop tools around the orchestration engine designer by rehosting andcustomizing the design surface. The framework of the invention expectsthe hosting container application to provide a set of services such aseditors and/or text buffers.

One step in rehosting the designer is to create a loader and a designsurface. The loader is responsible for loading a XOML file andconstructing the designer host infrastructure which maintains theactivities. The design surface maintains the designer hostinfrastructure within it and provides services to host and interact withthe design surface. The design surface acts as a service container aswell as a service provider. In one example, the following code isexecuted to load a XOML document and construct a designer host whichmaintains the activities in it.

this.loader.XomlFile = filePath; if (this.surface.IsLoaded == false)this.surface.BeginLoad(this.loader);

The following services enable different functions in the designer. AnISelectionService function maintains the selected objects. AnIToolboxService function manages interaction with the toolbox. AnIMenuCommandService function manages interaction with the menu. AnITypeProvider function enables the type system. In addition, there maybe additional services provided by the designer hosting environment toenable advanced designer features.

The type system is a component in the component model framework of theinvention. When a designer is hosted inside a project system, aTypeProvider object is created on a per project basis. Assemblyreferences in the project are pushed to the type provider. Further, theuser code files in the project are parsed and a single code compile unitis created and pushed to the type provider. Also, the invention listensto the events in the project system which may cause the types to bechanged in the type system and makes appropriate calls to the typeprovider to re-load types in response to the changes.

Undo/Redo

After creating and correctly constructing a schedule, a developer maywish to roll-back a series of performed operations. Undo and redofunctions of the invention provide visual feedback illustrating whichactivity has been directly affected. For example, when a property changeon an activity is undone, the activity which was affected becomesselected. When the deletion of multiple objects is undone, all theobjects involved become selected when they are restored to the schedule.Undo/Redo is a common feature used throughout many applications in otherfields and its meaning is well understood. In the orchestration enginedesigner, undo/redo items are not purged on Save. Further, undo/redo maybe performed in the process/workflow view, XOML view, when a developerswitches between views, and in the code beside.

Undo/Redo is provided for the following actions in the process/workflowview: activity drag and drop (e.g., dragging an activity from thetoolbox to the design surface, moving an activity from one part of theschedule to another, and moving an activity from one designer toanother), configuration of an activity (e.g., specifying properties foran activity), and cut/copy/paste/delete.

In one embodiment, the serialized view (e.g., XOML view) is an XMLeditor which provides the standard undo/redo operations of a texteditor. The designer of the invention provides feedback to the developerindicating that changes made in the process/workflow view and thenundone in serialized view will result in the loss of serialized code.When the developer constructs a portion of the schedule in theprocess/workflow view, switches to the serialized view and then decidesto perform a undo/redo operation, a warning will appear.

Exemplary Operating Environment

FIG. 10 shows one example of a general purpose computing device in theform of a computer 130. In one embodiment of the invention, a computersuch as the computer 130 is suitable for use in the other figuresillustrated and described herein. Computer 130 has one or moreprocessors or processing units 132 and a system memory 134. In theillustrated embodiment, a system bus 136 couples various systemcomponents including the system memory 134 to the processors 132. Thebus 136 represents one or more of any of several types of busstructures, including a memory bus or memory controller, a peripheralbus, an accelerated graphics port, and a processor or local bus usingany of a variety of bus architectures. By way of example, and notlimitation, such architectures include Industry Standard Architecture(ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA)bus, Video Electronics Standards Association (VESA) local bus, andPeripheral Component Interconnect (PCI) bus also known as Mezzanine bus.

The computer 130 typically has at least some form of computer readablemedia. Computer readable media, which include both volatile andnonvolatile media, removable and non-removable media, may be anyavailable medium that may be accessed by computer 130. By way of exampleand not limitation, computer readable media comprise computer storagemedia and communication media. Computer storage media include volatileand nonvolatile, removable and non-removable media implemented in anymethod or technology for storage of information such as computerreadable instructions, data structures, program modules or other data.For example, computer storage media include RAM, ROM, EEPROM, flashmemory or other memory technology, CD-ROM, digital versatile disks (DVD)or other optical disk storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium that may be used to store the desired information and that may beaccessed by computer 130. Communication media typically embody computerreadable instructions, data structures, program modules, or other datain a modulated data signal such as a carrier wave or other transportmechanism and include any information delivery media. Those skilled inthe art are familiar with the modulated data signal, which has one ormore of its characteristics set or changed in such a manner as to encodeinformation in the signal. Wired media, such as a wired network ordirect-wired connection, and wireless media, such as acoustic, RF,infrared, and other wireless media, are examples of communication media.Combinations of any of the above are also included within the scope ofcomputer readable media.

The system memory 134 includes computer storage media in the form ofremovable and/or non-removable, volatile and/or nonvolatile memory. Inthe illustrated embodiment, system memory 134 includes read only memory(ROM) 138 and random access memory (RAM) 140. A basic input/outputsystem 142 (BIOS), containing the basic routines that help to transferinformation between elements within computer 130, such as duringstart-up, is typically stored in ROM 138. RAM 140 typically containsdata and/or program modules that are immediately accessible to and/orpresently being operated on by processing unit 132. By way of example,and not limitation, FIG. 10 illustrates operating system 144,application programs 146, other program modules 148, and program data150.

The computer 130 may also include other removable/non-removable,volatile/nonvolatile computer storage media. For example, FIG. 10illustrates a hard disk drive 154 that reads from or writes tonon-removable, nonvolatile magnetic media. FIG. 10 also shows a magneticdisk drive 156 that reads from or writes to a removable, nonvolatilemagnetic disk 158, and an optical disk drive 160 that reads from orwrites to a removable, nonvolatile optical disk 162 such as a CD-ROM orother optical media. Other removable/non-removable, volatile/nonvolatilecomputer storage media that may be used in the exemplary operatingenvironment include, but are not limited to, magnetic tape cassettes,flash memory cards, digital versatile disks, digital video tape, solidstate RAM, solid state ROM, and the like. The hard disk drive 154, andmagnetic disk drive 156 and optical disk drive 160 are typicallyconnected to the system bus 136 by a non-volatile memory interface, suchas interface 166.

The drives or other mass storage devices and their associated computerstorage media discussed above and illustrated in FIG. 10, providestorage of computer readable instructions, data structures, programmodules and other data for the computer 130. In FIG. 10, for example,hard disk drive 154 is illustrated as storing operating system 170,application programs 172, other program modules 174, and program data176. Note that these components may either be the same as or differentfrom operating system 144, application programs 146, other programmodules 148, and program data 150. Operating system 170, applicationprograms 172, other program modules 174, and program data 176 are givendifferent numbers here to illustrate that, at a minimum, they aredifferent copies.

A user may enter commands and information into computer 130 throughinput devices or user interface selection devices such as a keyboard 180and a pointing device 182 (e.g., a mouse, trackball, pen, or touch pad).Other input devices (not shown) may include a microphone, joystick, gamepad, satellite dish, scanner, or the like. These and other input devicesare connected to processing unit 132 through a user input interface 184that is coupled to system bus 136, but may be connected by otherinterface and bus structures, such as a parallel port, game port, or aUniversal Serial Bus (USB). A monitor 188 or other type of displaydevice is also connected to system bus 136 via an interface, such as avideo interface 190. In addition to the monitor 188, computers ofteninclude other peripheral output devices (not shown) such as a printerand speakers, which may be connected through an output peripheralinterface (not shown).

The computer 130 may operate in a networked environment using logicalconnections to one or more remote computers, such as a remote computer194. The remote computer 194 may be a personal computer, a server, arouter, a network PC, a peer device or other common network node, andtypically includes many or all of the elements described above relativeto computer 130. The logical connections depicted in FIG. 10 include alocal area network (LAN) 196 and a wide area network (WAN) 198, but mayalso include other networks. LAN 136 and/or WAN 138 may be a wirednetwork, a wireless network, a combination thereof, and so on. Suchnetworking environments are commonplace in offices, enterprise-widecomputer networks, intranets, and global computer networks (e.g., theInternet).

When used in a local area networking environment, computer 130 isconnected to the LAN 196 through a network interface or adapter 186.When used in a wide area networking environment, computer 130 typicallyincludes a modem 178 or other means for establishing communications overthe WAN 198, such as the Internet. The modem 178, which may be internalor external, is connected to system bus 136 via the user input interface184, or other appropriate mechanism. In a networked environment, programmodules depicted relative to computer 130, or portions thereof, may bestored in a remote memory storage device (not shown). By way of example,and not limitation, FIG. 10 illustrates remote application programs 192as residing on the memory device. The network connections shown areexemplary and other means of establishing a communications link betweenthe computers may be used.

Generally, the data processors of computer 130 are programmed by meansof instructions stored at different times in the variouscomputer-readable storage media of the computer. Programs and operatingsystems are typically distributed, for example, on floppy disks orCD-ROMs. From there, they are installed or loaded into the secondarymemory of a computer. At execution, they are loaded at least partiallyinto the computer's primary electronic memory. The invention describedherein includes these and other various types of computer-readablestorage media when such media contain instructions or programs forimplementing the steps described below in conjunction with amicroprocessor or other data processor. The invention also includes thecomputer itself when programmed according to the methods and techniquesdescribed herein.

For purposes of illustration, programs and other executable programcomponents, such as the operating system, are illustrated herein asdiscrete blocks. It is recognized, however, that such programs andcomponents reside at various times in different storage components ofthe computer, and are executed by the data processor(s) of the computer.

Although described in connection with an exemplary computing systemenvironment, including computer 130, the invention is operational withnumerous other general purpose or special purpose computing systemenvironments or configurations. The computing system environment is notintended to suggest any limitation as to the scope of use orfunctionality of the invention. Moreover, the computing systemenvironment should not be interpreted as having any dependency orrequirement relating to any one or combination of components illustratedin the exemplary operating environment. Examples of well known computingsystems, environments, and/or configurations that may be suitable foruse with the invention include, but are not limited to, personalcomputers, server computers, hand-held or laptop devices, multiprocessorsystems, microprocessor-based systems, set top boxes, programmableconsumer electronics, mobile telephones, network PCs, minicomputers,mainframe computers, distributed computing environments that include anyof the above systems or devices, and the like.

The invention may be described in the general context ofcomputer-executable instructions, such as program modules, executed byone or more computers or other devices. Generally, program modulesinclude, but are not limited to, routines, programs, objects,components, and data structures that perform particular tasks orimplement particular abstract data types. The invention may also bepracticed in distributed computing environments where tasks areperformed by remote processing devices that are linked through acommunications network. In a distributed computing environment, programmodules may be located in both local and remote computer storage mediaincluding memory storage devices.

An interface in the context of a software architecture includes asoftware module, component, code portion, or other sequence ofcomputer-executable instructions. The interface includes, for example, afirst module accessing a second module to perform computing tasks onbehalf of the first module. The first and second modules include, in oneexample, application programming interfaces (APIs) such as provided byoperating systems, component object model (COM) interfaces (e.g., forpeer-to-peer application communication), and extensible markup languagemetadata interchange format (XMI) interfaces (e.g., for communicationbetween web services).

The interface may be a tightly coupled, synchronous implementation suchas in Java 2 Platform Enterprise Edition (J2EE), COM, or distributed COM(DCOM) examples. Alternatively or in addition, the interface may be aloosely coupled, asynchronous implementation such as in a web service(e.g., using the simple object access protocol). In general, theinterface includes any combination of the following characteristics:tightly coupled, loosely coupled, synchronous, and asynchronous.Further, the interface may conform to a standard protocol, a proprietaryprotocol, or any combination of standard and proprietary protocols.

The interfaces described herein may all be part of a single interface ormay be implemented as separate interfaces or any combination therein.The interfaces may execute locally or remotely to provide functionality.Further, the interfaces may include additional or less functionalitythan illustrated or described herein.

The order of execution or performance of the methods illustrated anddescribed herein is not essential, unless otherwise specified. That is,elements of the methods may be performed in any order, unless otherwisespecified, and that the methods may include more or less elements thanthose disclosed herein. For example, it is contemplated that executingor performing a particular element before, contemporaneously with, orafter another element is within the scope of the invention.

When introducing elements of the present invention or the embodiment(s)thereof, the articles “a,” “an,” “the,” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions, products,and methods without departing from the scope of the invention, it isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

APPENDIX A

Exemplary Activities and Exemplary Implementation Thereof

Exemplary activities include the following: Send, SendRequest,SendResponse, Receive, ReceiveRequest, ReceiveResponse, Code, Delay,Fault, Suspend, Terminate, InvokeSchedule, InvokeSchedules,InvokeWebService, DotNetEventSource, DotNetEventSink, Sequence,Parallel, While, ConditionalBranch, Conditional, Constrained,ConstrainedActivityGroup (CAG), EventDriven, Listen, EventHandlers,ExceptionHandler, ExceptionHandlers, Compensate, CompensationHandler,Scope, and Schedule.

Each of the exemplary activities have metadata associated therewith. Themetadata is transferred to a declarative representation of the workflowby the serializer associated with the activity. For example, themetadata may include an optional code-beside method and an optionalcollection of correlation sets.

Send Activities

The orchestration engine provides three activities (e.g., Send,SendRequest, and SendResponse) for sending messages, each of whichaddresses a different use case. Additionally, because the threeactivities share some metadata, an abstract base class is defined andused as the superclass of all three.

Receive Activities

The orchestration engine provides three activities (e.g., Receive,ReceiveRequest, and ReceiveResponse) for receiving messages, each ofwhich addresses a different use case. Additionally, because the threeactivities share some metadata, an abstract base class is defined andused as the superclass of all three.

Code

The Code activity executes the code-beside method indicated in themetadata.

Delay

The Delay activity executes its mandatory code-beside method to generatea DateTime value. It internally sets the TimeoutValue property on itsinstance data to this value. If the DateTime is in the past, the Delaycompletes immediately. Otherwise, it sets up a timer subscription sothat the Delay will be notified when the timer fires. When the timerfires, the Delay is notified and it completes.

Fault

The Fault activity executes its mandatory code-beside method to generatea Exception object. It then throws this exception.

Suspend

The Suspend activity suspends the current schedule instance.

Terminate

The Terminate activity terminates the current schedule instance.

Invoke Schedule

The InvokeSchedule activity invokes a schedule.

Invoke Web Service

Invokes a web service via a proxy class, passing and receivingparameters as specified.

DotNetEvent Sink

Blocks awaiting notification that the specified event has been raised bya previously invoked schedule instance.

DotNetEvent Source

Raises the specified event, and immediately completes execution.

Sequence

The Sequence activity coordinates the execution of a set of childactivities in an ordered fashion, one at a time.

Parallel

The Parallel activity executes a set of child activities concurrently.

While

Iteratively executes the child activity.

ConditionalBranch

Executes the child activities, per Sequence semantics.

Conditional

A Conditional activity contains an ordered set of ConditionalBranchactivities.

Constrained

Wrap an activity for the purpose of adding it to a constrained activitygroup (CAG).

Metadata:

An enable rule for the wrapped activity.

A disable rule for the wrapped activity.

Runtime Properties:

Integer indicating whether the wrapped activity has completed at leastonce.

Execution:

The only allowed parent of a Constrained activity is a CAG. The CAGitself utilizes the enable and disable rules on a Constrained activityto determine when to execute it. When the Constrained activity is toldby the CAG to execute, it simply executes the activity that it wraps.

The Performed property is incremented when the Constrained activitycompletes its execution. It is reset to zero only when the parent CAGitself is re-executed (e.g. within a WhileLoop or a second, outer, CAG).

CAG (Constrained Activity Group)

Provide constraint-based execution of a set of child constrainedactivities.

Metadata:

A completion rule.

Execution:

CAG contains only constrained activities. When the CAG executes, itexecutes (and re-executes) child activities based upon the evaluation oftheir enable and disable constraints. A child activity is executed bythe CAG only when its enable rule evaluates to true and its disable ruleevaluates to false. In one embodiment, CAG walks its sub-tree andsubscribes to activity state changes for all activities (this will stopat call boundaries). CAG adds a subscription whenever an activity isadded dynamically to its sub-tree. CAG subscribes to data changes forits enclosing scope and all parent scopes up to a schedule boundary.These subscriptions are determined by analysis of the enable and disablerules on all constrained activities in the CAG. The engine deliversbatched notifications of data changes and the CAG decides which rules toevaluate. Note that data changes made by a called schedule are postedwhen the call completes. The invention further identifies scope variabledependencies even if those variables are accessed indirectly via codebeside methods. As such, it is possible to be very specific indetermining which constraints should be reevaluated when a variable ischanged. This same mechanism works for both declarative and code rules.If a constrained activity has no enable rule, it is taken to always betrue. If a constrained activity has no disable rule, it is taken toalways be Performed>0. Thus, if no rules are specified on a constrainedactivity, it is executed immediately when the CAG executes, and it doesnot ever get re-executed. Likewise, if only a custom enable rule isprovided on a constrained activity, it is executed when that enable ruleevaluates to true and it only executes that one time. Ifconstraint-based re-execution is desired, an appropriate custom disablerule should be provided along with the appropriate enable rule. Thefollowing table illustrates the condition required to execute aConstrained activity.

TABLE A1 Constrained Activity Execution. EnableRule DisableRule Canactivity execute? TRUE FALSE Yes TRUE TRUE No FALSE FALSE No FALSE TRUENo

If during the execution of an activity, the disable rule for thatactivity evaluates to true, the CAG cancels the execution of thatactivity. This does not preclude re-execution of that activity. As soonas the completion rule of the CAG evaluates to true, the CAG immediatelycancels any currently executing child activities, and then itselfcompletes. Rules (e.g., enable, disable, and completion) are evaluatedwhenever necessary based upon their data and state change dependencies.

The CAG provides two operation modes: Preview & Edit. If the CAGdesigner is in preview mode, the developer is only able to select theactivity which appears the filmstrip. The property browser exposesenable and disable rule options when a developer has selected anyactivity. This allows a developer to set enable and disable rules foreach activity with a CAG. If the CAG designer is in design mode, thedeveloper is able to click on the activity in the preview window (calleda Constrained). The property browser displays the enable and disablerule options (e.g. similar to preview mode) in addition to theproperties normally exposed by the specific activity. The CAG designerprovides the additional context menu options shown below.

-   -   Preview Activity: Given a selected activity, the CAG switches        from design mode to preview mode.    -   Edit Activity Given a selected activity, the CAG switches from        preview mode to design mode.    -   View Previous Activity: Move to the activity immediately        preceding the currently selected activity in the filmstrip. When        you reach the first activity in the CAG filmstrip, this menu        option is disabled.    -   View Next Activity: Move to the activity immediately following        the currently selected activity in the filmstrip. When you reach        the last activity in the CAG filmstrip, this menu option is        disabled.

In one embodiment, each activity within a CAG is wrapped within a‘constrained activity.’ This is then exposed to the developer via thefilmstrip of the CAG. If the CAG is in preview mode and a developerselects this activity and copies it, the only place where it may bepasted (and thus have the consequential context menu enabled) in oneembodiment is within another CAG. However, if the developer switches theCAG mode to “Design” and chooses the activity within the preview pane,copy, paste, and drag-drop are enabled in a similar manner as with theother activities.

Task

Model an external unit of work that is performed by one or moreprincipals.

Event Driven

Wrap an activity whose execution is triggered by an “event” activity.

Listen

Conditionally execute one of n child EventDriven activities.

Event Handlers

The EventHandlers activity simply holds a set of EventDriven activities,for use by the associated Scope.

Exception Handler

Wraps an activity with metadata that represents a catch block for ascope.

Exception Handlers

Wrap an ordered set of ExceptionHandler activities.

Compensate

Compensate a completed child scope.

Compensation Handler

Wrap a child activity that is defined as the compensation handler for ascope.

Scope

A scope is: a transaction boundary; an exception handling boundary; acompensation boundary; an event handling boundary; and, a boundary formessage, variable, correlation set, and channel declarations (i.e.shared data state). Execution of the activities within a Scope issequential, and thus the contained activities are explicitly orderedwhen the scope is constructed, as in a Sequence.

Schedule

A Schedule is the only top-level activity that the orchestration enginewill execute.

Composite Activities

The composite activity types that enable control flow are: Sequence,Parallel, Constrained Activity Group, Conditional, While, Listen.Additionally, Scope and Schedule are composite activity types that actas containers with implied sequencing of the activities within them.

1. A computer-implemented method for modeling a workflow, said workflowrepresenting a business process, said method comprising: presenting aplurality of activities to a user; receiving from the user a firstselection of the activities and a flow specification associatedtherewith; grouping, by a computer, the received first selection ofactivities; receiving, by the computer, from the user another selectionof the activities and a constraint associated with each of theactivities from the other selection, said constraint including afunction that enables the activity associated therewith for executionwhen the constraint is satisfied, said activities from the receivedfirst selection being different from the activities from the otherselection; and generating, by the computer, a constrained activity group(CAG) including one or more of the activities from the other selection,said CAG defining at least one of the following conditions for the oneor more of the activities from the other selection in the CAG: theconstraint can be disabled at any time after the constraint has beenenabled; when an enabled constraint becomes true, the enabled constraintdeclares that the activity associated therewith is ready for executionand must be enabled; when a completion condition of an executingactivity is evaluated to be true at any time, any and all executingactivities contained within the CAG are immediately canceled; merging,by the computer, the received other selection of the activities with thegrouped selection of activities to create a workflow; executing, by thecomputer, the activities from the first selection in the mergedworkflow; during executing the activities from the first selection,determining, by the computer, a change in the constraint for each of theactivities from the other selection in the merged workflow, said changeresulting from changes to data in the function included in theconstraint; and enabling, by the computer, the execution of each of theactivities from the other selection in the CAG when the constraintassociated therewith is satisfied as a function of the determinedchange, wherein a course of execution of the merged workflow is guidedby the constraints associated with the activities from the otherselection of the user contained within the CAG.
 2. The method of claim1, wherein grouping the received first selection of activities occurs inaccordance with the received flow specification, said received firstselection of activities being well-defined control flow activities thatare processed based on the flow specification and that are complete whenan endpoint for the activities is reached.
 3. The method of claim 1,wherein each of the activities from the other selection is an activitythat is executed not based on the flow specification, is executed in anyorder, and is executed whenever the constraint associated with anactivity from the other selection is satisfied.
 4. The method of claim1, wherein executing the activities from the first selection in themerged workflow occurs according to the flow specification.
 5. Themethod of claim 1, further comprising defining the constraint.
 6. Themethod of claim 1, further comprising executing the created workflow by:evaluating the constraint; and executing the activities from the otherselection as a function of said evaluating.
 7. The method of claim 1,further comprising executing the created workflow by executing theactivities with the received selection of activities in accordance withthe flow specification.
 8. The method of claim 1, wherein presenting theplurality of activities to the user comprises displaying the pluralityof activities on a display.
 9. A system comprising a plurality ofcomputer executable components tangibly embodied on computer-readablestorage media that, when executed by a computer, model a workflow havinga flow-based region and a constraint-based region, said systemcomprising: a display component for presenting a plurality of activitiesto a user; an interface component for receiving from the user a firstselection of the activities, said interface component further receivingfrom the user another selection of the activities and a constraintassociated with each of the activities from the other selection, saidconstraint for each of the activities associated therewith from theother selection including a function that enables the activities forexecution when the constraint is satisfied, said activities of thereceived first selection being different from the activities of theother selection; and a designer component for grouping the receivedselection of activities in accordance with the received flowspecification, said designer component generating a constrained activitygroup (CAG) including one or more of the activities from the otherselection, said CAG defining at least one of the following conditionsfor the one or more of the activities from the other selection in theCAG: the constraint can be disabled at any time after the constraint hasbeen enabled; when an enabled constraint becomes true, the enabledconstraint declares that the activity associated therewith is ready forexecution and must be enabled; when a completion condition of anexecuting activity is evaluated to be true at any time, any and allexecuting activities contained within the CAG are immediately canceled,said designer component further merging the received other selection ofthe activities with the grouped selection of activities to create aworkflow; wherein the designer component determines a change in theconstraint in each of the activities from the other selection in themerged workflow during executing the activities from the firstselection, said change resulting from changes to data in the functionincluded in the constraint; and wherein the designer component enablesthe execution of each of the activities from the other selection in theCAG when the constraint associated therewith is satisfied as a functionof the determined change, wherein a course of execution of the mergedworkflow is guided by the constraints associated with the activitiesfrom the other selection of the user contained within the CAG.
 10. Thesystem of claim 9, wherein the interface component has a flowspecification associated therewith.
 11. The system of claim 9, saidreceived first selection of activities being well-defined control flowactivities that are processed based on the flow specification and thatare complete when an endpoint for the activities is reached.
 12. Thesystem of claim 9, wherein each of the activities from the otherselection is an activity that is executed not based on the flowspecification, is executed in any order, and is executed whenever theconstraint associated with each of the activities from the otherselection is satisfied.
 13. The system of claim 9, wherein the designercomponent presents the activities from the first selection in the mergedworkflow according to the flow specification.
 14. The system of claim 9,further comprising a runtime component for executing the createdworkflow by: evaluating the constraint; and executing the activitiesfrom the other selection of the activities as a function of saidevaluating.
 15. The system of claim 9, further comprising a runtimecomponent for executing the created workflow by executing the activitiesfrom the received selection of activities in accordance with the flowspecification.
 16. The system of claim 9, wherein the display component,interface component, and the designer component execute within anexecution environment of an application program.
 17. The system of claim9, wherein the constraint comprises a completion semantic.